Distribution and status of the hippopotamids in the Ivory Coast

Abstract

The distribution and relative abundance of the common hippo (Hippopotamus amphibius) and the pygmy hippo (Hexaprotodon liberiensis) was studied in the Ivory Coast between 1978 and 1986 by questionnaire survey, interviews, local field investigations and aerial censuses. In addition, the size of the pygmy hippo  population in the Tai Forest area was monitored between 1995 and 2001. At the time of the initial study, the common hippo inhabited the Sassandra, Bandama and Comoé rivers, but was abundant only in the Upper Comoé. The pygmy hippo was restricted to the Guinean Forest zone between 7°25’N (Tiapleu Forest Reserve (Forêts Classée)) in the north and 4°18’W (estuary of the Agnebi River) in the east, where it was abundant in undisturbed rainforest areas. Population data are presented from the Comoé, Tai and Azagny national parks where the ecology of both species was studied in greater detail. The total popu lation of the common hippopotamus was estimated at about 1100 animals in 1978 1984, of which at least 70%  concentrated during the dry season in the Upper Comoé, Leraba and Iringou rivers. The average dry season population density in the Comoé varied at that time between three and four animals per river kilometre, in groups of five to six, but had dropped to one to two per kilometre in 2002. During the rainy season hippos disperse upstream into smaller tributaries and downstream as far as the coast. As the forest zone is modified by forestry and agriculture, small herds of common hippos have become resident and in some localities are sympatric with the pygmy hippo. Pygmy hippos are solitary animals, confined to home ranges of 50 150 ha. In optimal habitat their population density can be as high as seven animals/km²,  averaging about three animals/km2 over larger areas of undisturbed rainforest. At present, however, hunting pressure has reduced population densities to 0.8 2.5 animals/km² even in the most favourable ecological conditions of the Tai National Park.   Extrapolation of these densities suggests that the total population of pygmy hippos in the Ivory Coast is greater than previously thought, but does not exceed 15 000 animals. Most of these inhabit the Tai National Park and its adjacent protected areas. The remainder occur mainly in various forest reserves (Forêts classées). Ecological factors, which influence population density or limit pop ulation growth of the two different hippo species, are discussed and recommendations made for their conservation.

Key words: Hippopotamus amphibius, Hexaprotodon liberiensis, Ivory Coast.